Hello Shifeng, Riak uses Bitcask as its default data backend, it may also use leveldb as a backend but must be configured to do so[0][1]. Both bitcask[2] and leveldb[3] do not reclaim disk space immediately when a delete is issued. Incidentally, neither do updates. Because Riak is non-destructive, aka append only, aka no in-place updates, mutation operations like updates or deletes are actually writes. For example, a 10KB object that is updated four times in some short interval will consume 50KB space (original 10KB + 4 x 10KB updates) until merge/compaction occurs. A delete is actually a special zero byte value write indicating a key is marked for deletion, aka a tombstone. Bitcask will reclaim disk space via merge operations which may be controlled by the user. Leveldb reclaims disk space via compaction operations.
Architects and Developers should take into account their update/delete ratios and consider how those will affect disk space consumption and consider how deletes operate in distributed systems in general and Riak in specific from an application perspective. John Daily wrote a must read four part series on Riak's configurable behaviors that all Riak developers should be familiar with. Part 3 deals specifically with delete related considerations[4]. Thank you, Alexander [0] http://docs.basho.com/riak/kv/latest/setup/planning/backend/leveldb/#installing-eleveldb [1] http://docs.basho.com/riak/kv/latest/configuring/backend/ [2] http://docs.basho.com/riak/kv/latest/setup/planning/backend/bitcask/ [3] http://docs.basho.com/riak/kv/latest/setup/planning/backend/leveldb/ [4] http://basho.com/posts/technical/riaks-config-behaviors-part-3/ On Wed, Apr 20, 2016 at 8:17 AM, Daniel Abrahamsson <daniel.abrahams...@klarna.com> wrote: > Hi, > > What riak version and what riak backend are you using? For leveldb you have > to take compaction into account, and for older bitcask versions there are > known issues with data not being properly deleted. > > //Daniel > > _______________________________________________ > riak-users mailing list > riak-users@lists.basho.com > http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com > _______________________________________________ riak-users mailing list riak-users@lists.basho.com http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
